Hitherto, a thrust bearing which is disposed to face a thrust collar provided in a rotation shaft is known as a bearing for a high-speed rotation body. As such a thrust bearing, a foil type thrust bearing, that is, a thrust foil bearing, is known. In the thrust foil bearing, a bearing surface is formed by a flexible foil (a metallic thin plate) to absorb the motion of the rotation shaft (the axial displacement or inclination of the thrust collar) caused by a vibration or an impact, and a foil structure is provided below the bearing surface to flexibly support the bearing surface.
As one of such thrust foil bearings, a structure is known in which a bearing surface is formed by a plurality of circular ring (annular) plate-shaped foil pieces (top foil pieces) obtained by dividing an annular plate in the circumferential direction by cutting, and these top foil pieces are supported by corrugated foil pieces (bump foil pieces) (for example, see Patent Documents 1, 2, and 3). Each top foil piece (having a thickness of about 100 μm) has an inclination angle with respect to a thrust collar, and thus a bearing gap between the thrust collar and the top foil piece is formed in a wedge shape in the side view. That is, the bearing gap is formed to be narrowed from an upstream side toward a downstream side in the rotation direction of the thrust collar (the rotation shaft). Thus, when the thrust collar rotates from a side having a wide bearing gap (an upstream side) toward a side having a narrow bearing gap (a downstream side), a lubricating fluid flows into a wedge and load capacity is exerted.
Only an upstream end edge of the top foil piece in the rotation direction of the thrust collar (the rotation shaft) is fixed to a base plate. Then, when a bearing load increases, the top foil becomes horizontal while being inclined with a fixed edge (an upstream end edge) as a support point and maximum load capacity is exerted at the time of an inclination angle of about 0.10. The bump foil piece is disposed so that a ridge line of a peak becomes parallel to a downstream end edge of the top foil piece and only a downstream end edge of the bump foil piece in the rotation direction of the thrust collar (the rotation shaft) is fixed to the base plate. That is, the upstream end edge is a free end.
Since a pressure of a fluid lubricating film generated in the top foil piece increases at the side having a narrow bearing gap (the downstream side), the bump foil piece is disposed and fixed in this way to support this portion with high rigidity, whereby high load capacity is obtained.